Furan reimpregnation resin

ABSTRACT

There are disclosed polymers containing tungsten chemically bonded in the polymer chain. The polymers are obtained by reacting 2-furanacrylic acid or 2-furoic acid with the reaction product of tungsten carbonyl with pyrrolidine. These polymers are useful as multi-cycle reimpregnation resins.

This is a division of application Ser. No. 479,926 filed Mar. 29, 1983,now U.S. Pat. No. 4,540,764

BACKGROUND OF THE INVENTION

This invention relates to thermosetting, solventless polymers containingvariable ratios of tungsten to carbon atoms chemically bonded in thepolymer chain which are particularly useful for multi-cyclereimpregnation of a carbon/carbon composite.

With the advent of aerospace products, carbon/carbon composites havinghigh densities have come into widespread use. One or a combination ofthe following three methods for densification of carbon/carboncomposites are commonly employed: (1) high temperature consolidation;(2) chemical vapor deposition; and (3) multi-cycle reimpregnation. Forapplications involving large parts or complex shapes, multi-cyclereimpregnation has been found to be the most effective method forimparting oxidation resistance and energy absorbing characteristicsthrough the use of specifically formulated polymers.

A reimpregnation resin is a thermosetting polymer introduced as a liquidinto the characteristic void of a carbon/carbon composite. The resin issubsequently cured and heat treated, thus increasing the density of thecomposite. Selected polymers impart specific desired characteristics tothe composite depending upon the ultimate application. Viablereimpregnation resins must maintain a suitably low viscosity during thereimpregnation process and, in addition, exhibit a relatively high charyield. "Multi-cycle reimpregnation" is the term applied when thereimpregnation process is repeated a number of times.

U.S. Pat. No. 4,185,043 to Robert C. Shaffer discloses thermoplastic andthermosetting polymers which incorporate tungsten and/or molybdenummetal atoms. The metal atoms are incorporated into the polymer byreacting a monomer or polymer containing at least one free carboxylgroup with a reaction product of tungsten or molybdenum carbonyl andpyrrolidine to obtain a polymer. It is disclosed that the polymers areuseful as reimpregnation resins. However, the polymers disclosed in theabove patent are not specifically designed for use as multi-cyclereimpregnation polymers.

SUMMARY OF THE INVENTION

It has now been discovered that suitable multi-cycle reimpregnationpolymers may be prepared by reacting 2-furanacrylic acid or 2-furoicacid with the reaction product of tungsten carbonyl and pyrrolidine. Thedark viscous polymer thus obtained may be utilized neat or it may becopolymerized with furfuryl alcohol or a dienophilic ester or to obtaina variable metal content containing thermosetting multi-cyclereimpregnation resin. Because of the relatively low viscosity atmoderate temperatures, the polymers of this invention may be used in amulti-cycle reimpregnation process without a solvent. Further, byappropriate choice of the amounts of reactants, precise variation intungsten content is achieved while retaining the tungsten in atomic formin the polymer molecule. For maximum metal loading, the furan basedpolymer containing chemically bonded tungsten atoms in the polymer chainmay be used neat in a multi-cycle reimpregnation process.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In order to prepare the polymers of this invention, a complex is firstprepared by reacting tungsten carbonyl with pyrrolidine. The reactionbetween the tungsten carbonyl and pyrrolidine may be accomplished in oneof several methods found in the literature, e.g., an article by Fowleset al entitled "The Reactions Of Group VI Metal Carbonyls WithPyrrolidine, Piperazine and Morpholine", Inorganic Chemistry, Vol. 3,No. 2, 1964, pages 257-259. The reaction product consisting of thepyrrolidine-tungsten carbonyl complex is ground to a fine powder forsubsequent reaction. The reaction product of the pyrrolidine-tungstencarbonyl complex is believed to contain at least two moles ofpyrrolidine to one mole of tungsten carbonyl.

The 2-furanacrylic acid or 2-furoic acid is reacted with thepyrrolidine-tungsten carbonyl reaction product by combining the twomaterials and heating the reaction mixture, preferably within the rangeof about 150° to 160° C. for from about two to four hours. The amount ofpyrrolidine-tungsten carbonyl reaction product which is reacted with theacid may vary widely. Preferably, about two moles of acid are reactedper mole of pyrrolidine-tungsten carbonyl reaction product. Therelatively low melting point of the furanacrylic acid and furoic acidpermit the synthesis of high metal containing polymers without the useof solvents. This property, coupled with the relatively low viscosityand high char yield of the tungsten containing polymers render thesepolymers particularly suitable for multi-cycle reimpregnation polymers.

The polymers of this invention have the property of being boththermoplastic and thermosetting, i.e., at temperature of up to about180° C. they are thermoplastic, i.e., they may be heated to obtain a lowviscosity flowable material which, upon cooling solidifies. At highertemperatures, i.e., above about 200° C., the materials arethermosetting, i.e., curable.

When it is desirable to obtain a lower amount of metal in themulti-cycle reimpregnation polymer, the polymers of this invention maybe copolymerized with another material such as furfuryl alcohol or adienophilic ester. The amount of metal in the finished resin may becontrolled by the ratio of polymer of this invention to prepolymer usedduring the copolymerization process. Dienophilic prepolymers which maybe polymerized with the tungsten containing polymers of this inventioninclude polyester prepolymers prepared by reacting an ethylenicallyunsaturated dicarboxylic acid or anhydride with a glycol.

The following examples illustrate the best mode contemplated forcarrying out this invention.

EXAMPLE 1

One mole equivalent of tungsten hexacarbonyl and an excess ofpyrrolidine are reacted to form the metal pyrrolidine complex. At thecompletion of the reaction, the product is washed and ground to a finepowder.

Two moles of 2-furanacrylic acid are added to one mole of thepyrrolidine-tungsten hexacarbonyl reaction product and the reagents arethen heated to 150°-160° C. for approximately three hours. A clear, darkorange polymer results. This is a thermoplastic material which is solidat room temperature. It may be used as a multi-cycle reimpregnationresin in a carbon/carbon composite by heating it to melt it and thenimpregnating it into the void of a carbon/carbon composite. The polymeris then cured by heating at 210° C. for 40 hours. This cured thermosetresin, when subsequently carbonized at 800° C. for one hour, containsapproximately 58% by weight.

EXAMPLE 2

Two moles of 2-furoic acid are heated until molten. One mole of thereaction product of tungsten hexacarbonyl and pyrrolidine obtained asdescribed in Example 1 is added with constant stirring. The reactantsare then heated to about 150° C. for two hours. A clear, dark, amberthermoplastic polymer results which is solid at room temperature. Thispolymer may be used as a multi-cycle reimpregnation polymer as describedin Example 1.

The following example illustrates the copolymerization of a polymer ofthis invention with a dienophilic prepolymer, i.e., an ethyleneglycol/maleic anhydride polyester prepolymer, in order to control themetal content of the resultant resin.

EXAMPLE 3

The polymer of Example 1, 496.00 g, is mixed with 143.52 g of furfurylalcohol and heated to approximately 60° C. in a four liter reactionkettle. The kettle is then removed from the mantle and 328.00 g of a 2:1molar ratio maleic anhydride/ethylene glycol prepolymer are mixedthoroughly with the reactants. The kettle is subsequently returned tothe mantle and heated to approximately 150-160° C. for a two hourperiod. The resulting product is a clear, dark, amber thermosettingresin which may be used as a multi-cycle reimpregnation resin for acarbon/carbon composite as previously described. When cured at 210° C.for 18 hours and subsequently carbonized at 800° C. for one hour, thereis obtained a char containing approximately 26% tungsten by weight.

What is claimed is:
 1. The copolymer obtained by copolymerizing furfurylalcohol, a polyester prepolymer prepared by reacting an ethylenicallyunsaturated dicarbocyclic acid or anhydride with a glycol or a mixtureof furfuryl alcohol and said polyester prepolymer with thethermoplastic/thermosetting product of (1) 2-furanacrylic acid or2-furoic acid and (2) a metal complex which is a reaction product oftungsten carbonyl with pyrrolidine, said copolymer being a multi-cyclereimpregnation polymer.
 2. A copolymer as defined in claim 1 wherein (1)is 2-furanacrylic acid.
 3. A copolymer as defined in claim 1 wherein (1)is 2-furoic acid.
 4. The copolymer of claim 2 wherein said polyesterprepolymer is a maleic anhydride/ethylene glycol prepolymer.
 5. Thecopolymer of claim 3 wherein said polyester prepolymer is a maleicanhydride/ethylene glycol prepolymer.
 6. The copolymer of claim 1wherein said polyester prepolymer is a maleic anhydride/ethylene glycolprepolymer.
 7. The copolymer of claim 2 wherein two moles of (1) arereacted per mole of pyrrolidine-tungsten carbonyl reaction product. 8.The copolymer of claim 3 wherein two moles of (1) are reacted per moleof pyrrolidine-tungsten carbonyl reaction product.
 9. The copolymer ofclaim 1 wherein two moles of (1) are reacted per mole ofpyrrolidine-tungsten carbonyl reaction product.
 10. The copolymer ofclaim 4 wherein two moles of (1) are reacted per mole ofpyrrolidine-tungsten carbonyl reaction product.
 11. The copolymer ofclaim 5 wherein two moles of (1) are reacted per mole ofpyrrolidine-tungsten carbonyl reaction product.
 12. The copolymer ofclaim 6 wherein two moles of (1) are reacted per mole ofpyrrolidine-tungsten carbonyl reaction product.